1. Field of the Invention
The present invention generally relates to clamping devices. More specifically, this invention relates to a tool clamping device adapted for engaging, clamping and supporting tooling in a manner that promotes automated tooling changes on a manufacturing production line.
2. Description of the Prior Art
Mechanical welding presses, or "welding knees", are commonly used on automated production assembly lines where multiple welds are necessary to join high volume subassemblies, such as automotive doors and hoods. Conventionally, as illustrated in U.S. Pat. No. 4,600,095 to Brems et al, a welding knee includes a very large machine frame having a lower movable platen, or table, and an upper workstation. The table is actuated vertically by specially designed straight-line lift linkages which are typically driven by a motion generating device powered by a reversible electric motor. The use of a generating device powered by an electric motor provides that the table is raised rapidly during an initial phase, then slows the table's rate of ascent during an intermediate phase, and again rapidly raises the table through a final stage in which the table becomes positioned immediately below the upper workstation. Brems et al illustrate these stages in FIGS. 1 through 4. During the intermediate stage, the table lifts a workpiece from a conveyor and raises it toward the upper workstation for the welding operation. It is not uncommon for the entire ascent of the table to cover approximately twenty inches of travel in one to two seconds.
The table is provided with lower tooling which is adapted to mate with upper tooling suspended from the upper workstation. The upper and lower tooling are designed to receive the workpiece in a manner that maintains the proper location of the components of the welded assembly prior to welding. The upper tooling includes welding guns which perform the welding operation. The number of welding guns will vary with the particular component being assembled, with as many as twenty welding guns being typical.
Each particular component being welded requires its own specific upper and lower tooling, therefore, tooling changes are a necessity in order that a machine such as the welding knee be fully utilized and versatile. In that the weight of the upper tooling can be considerable--with ten thousand pounds not being uncommon--precautions must be taken during a tooling change to ensure that the upper tooling is securely engaged and supported from the upper workstation, as well as being properly located on the upper workstation for alignment with the lower tooling. In the prior art, it has been the general practice to secure both the upper and lower tooling with bolts and other conventional fasteners directly to the respective table and upper workstation. While being adequate in terms of structural support, particular care must be used in raising the upper tooling into location below the upper workstation to properly position the upper tooling. Once in position, it can be extremely hazardous for the operator to secure the upper tooling in the conventional manner in that he or she must perform this task while the upper tooling is being positioned with a temporary support.
Accordingly, it would be far preferable to provide an automated mechanism, such as a specially adapted clamping device, to secure the upper tooling to the upper workstation. Clamping devices adapted for various operations are widely taught in the relevant art. As examples, U.S. Pat. No. 4,909,493 to Yonezawa teaches a hydraulically-actuated clamp cylinder for clamping a member that circumscribes the clamping cylinder; U.S. Pat. No. 4,892,623 to Reed teaches a solenoid-driven clamping device for clamping a cylindrical member; and U.S. Pat. No. 4,887,803 to Witt, U.S. Pat. No. 4,934,678 to Bernier, U.S. Pat. No. 4,968,247 to Olson and U.S. Pat. No. 5,005,813 to Lawrence teach clamping devices which are cam actuated. However, none of the clamping devices taught by the prior art are suitable for engaging and securing the upper tooling of a machine to the machine's upper workstation.
As can be readily appreciated by those skilled in the art, the above examples would require, at minimum, substantial modifications in order to be suitable for engaging and securing the upper tooling of a machine and particularly a welding knee. Even where possible, the durability and manner in which the clamping devices of the prior art operate would make the clampling devices unsuitable for use on an automated production assembly line where supporting 10,000 pounds presents a considerable safety concern.
In addition, it is generally preferable that the clamping device chosen for such a purpose be adapted to engage the upper tooling and properly align the upper tooling with the lower tooling during the clamping operation. This would allow the operator to place the upper tooling in the vicinity of the preferred clamping device, with the clamping device itself making the final movement which brings the upper tooling in alignment with the lower tooling.
From the above discussion, it can be readily appreciated that the prior art does not disclose a clamping device suitable for engaging and securing the upper tooling of a machine at its upper workstation. Nor does the prior art teach or suggest a clamping device which is adapted to be operated in an automated manner on a production assembly line to minimize the labor and time involved in changing the upper tooling.
Accordingly, what is needed is a motor-driven mechanical clamping device which is capable of engaging and lifting the upper tooling from a transport device and clamping the upper tooling in alignment with the lower tooling of a workstation in a manner which minimizes the labor and time required to install and remove the upper tooling, while also providing a clamping mechanism that will reliably secure and support the upper tooling throughout a production run.